Mechanisms of normal and abnormal pulmonary development

One of the prerequisites of life is the process of respiration in which an organism exchanges carbon dioxide for oxygen in order to obtain energy through the oxygenation of molecules containing carbon. The interfaces used by different organisms for gas exchange vary from simple diffusion between prokaryotic bacteria and the medium in which they reside, to a much more complex diffusible interface, namely a gas-exchanging organ also known as the lung used by higher eukaryotes, such as humans. The human lungs have an estimated 300.000.000 alveoli with a surface area of approximately 70 m2 by 0.1 flm in early adulthood (Comroe, 1965; Weibel, 1963) and is comprised of at least 40 differentiated cell types. The alveolar surface of the lung is surrounded by a capillary network that develops in close apposition. This enables gas exchange to occur with the blood that delivers the oxygen to the tissues. Therefore a 70 kg adult human can use 14.5 L oxygen per hour or 1020 molecules per second at rest. The oxygen demand can rise to approximately 330 L per hour during exercise (Comroe, 1965; Weibel, 1963). To establish such a highly complex organ, well-orchestrated cell interactions are required during development to generate a functional lung.